Search Results (160)

Ceramic oxide coatings were fabricated on 7075 aluminum alloy via micro-arc oxidation (MAO) in a silicate-phosphate electrolyte under voltages of 250 V, 300 V, and 350 V for 600 s. The effect of the applied voltage on the surface morphology, microstructure, phase composition, microhardness, roughness, coating thickness, and corrosion resistance was systematically studied. The coating obtained at 300 V demonstrated a dense structure with relatively low surface roughness (2.3 μm) and a thickness of approximately 70 μm. This sample also exhibited the most balanced performance, combining relatively high microhardness (~422 HV) and the lowest corrosion current density (6.1 × 10⁻⁷ A/cm²) in a 3.5 wt.% NaCl solution. X-ray diffraction patterns revealed the presence of both γ- and α-Al₂O₃ phases in all coated samples, with a relative increase in α-phase intensity observed at an intermediate voltage. The results demonstrate that the applied voltage plays a critical role in determining the coating structure and performance, offering insights into the surface treatment of high-strength aluminum alloys for engineering applications. Full article

In this work, micro-arc oxidation (MAO) under constant- and gradient-current modes was used to modify the surface of 6061 aluminum alloy. A black coating was created in situ on the alloy surface by controlling the spark discharge parameters during MAO. Using an electrochemical workstation (Metrohm Autolab, PGSTAT302 N, Herisau, Switzerland), energy-dispersive spectroscopy (EDS, JEOL, JSM-IT500A, Tokyo Metropolis, Japan), and scanning electron microscopy (SEM, JEOL, JSM-7900F, Tokyo Metropolis, Japan), the effects of the current output modes on the coating growth rate, energy consumption, colorimetric parameters (L*, a*, b*), microstructure, and corrosion resistance were methodically examined. The findings showed that the gradient-current mode (6 → 4 → 2 A/dm²) greatly lowered the micropore size (from 3.89 μm to 1.52 μm) and improved the coating compactness (porosity dropped by 40%), and all coatings satisfied the necessary blackness criterion (L* < 30). Additionally, this mode achieved excellent corrosion resistance, as demonstrated by a one-order-of-magnitude reduction in the corrosion current density (2.55 × 10⁻⁸ A/cm² vs. 2.34 × 10⁻⁷ A/cm²), while minimizing the energy consumption (2.37 kW·h/m²·μm vs. 3.45 kW·h/m²·μm for constant current). Full article

Due to their excellent mechanical properties and good biocompatibility, titanium (Ti) and its alloys are widely used as biomaterials. However, when implanted in the body, metallic materials may cause serious complications such as wear and infection, leading to patient discomfort and, in some cases, the need for revision surgery. Micro-arc oxidation (MAO) is a surface modification technique that offers a promising strategy to overcome these challenges. This study investigated the impact of the microstructure of Ti-25 Ta-xNb alloys (x = 10, 20, and 30 wt%) and the variation in applied voltage during the MAO process on the characteristics of the TiO₂ oxide coatings formed. The alloys were treated by MAO at 200, 250, and 300 V using a bioactive electrolyte containing Ca, P, Mg, and Ag. EDS, SEM, XRD, Raman spectroscopy, and adhesion tests performed characterization. Results indicated that Nb addition stabilized the β phase and anticipated the potentiostatic regime. Increasing the voltage supplied to the system provides greater energy, prolonging the galvanostatic regime and promoting the formation of larger and more uniform pores. The oxide coating thickness ranged from approximately 3 to 10 μm, with a tendency to decrease at higher voltages. The coatings exhibited low c, with anatase and rutile phases predominating, the applied voltage and Nb concentration influencing their relative proportions. Even in small amounts, all electrolyte elements (P, Mg, and Ag) were successfully incorporated into the coatings under all conditions. Raman and XRD analyses confirmed a decrease in anatase and an increase in rutile phases with increasing voltage and Nb content. Mechanical testing revealed good adhesion of the coatings in all samples, with the best results obtained at 200 V. The findings demonstrate that the developed coatings exhibit promising characteristics for future surface engineering strategies aimed at improving the performance of metallic biomaterials. Full article

A critical barrier to the clinical translation of biodegradable magnesium (Mg)-based materials lies in their rapid degradation rate in physiological environment, which leads to premature structural failure and compromised cytocompatibility. Micro-arc oxidation (MAO) coatings offer preliminary corrosion mitigation for Mg alloys, while their inherent structural porosity compromises long-term durability in physiological environment. To address this limitation, we developed a hierarchical coating system consisting of a dense Mg(OH)₂ interlayer (MAO/HT) superimposed on the MAO-treated substrate, followed by a functional polydopamine (PDA) topcoat to create a MAO/HT/PDA composite architecture. The surface characteristics and crystalline structures of these coatings were systematically characterized using field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD). The corrosion resistance and interfacsial stability in physiological environment were quantitatively assessed through electrochemical analyses and long-term immersion tests in simulated body fluid (SBF). The cytocompatibility of the coatings was assessed by directly culturing osteoblast on the coated samples. The results reveal that the Mg(OH)₂ film possesses a bulk-like structure and effectively seals the micro-pores of the MAO coating. The current density of MAO/HT/PDA sample decreases by two orders of magnitude compared to that of MAO sample, indicating excellent corrosion resistance. The PDA layer not only acts as a strong barrier to improve the corrosion performance of the coating but also helps maintain the stability of the coating, thus delaying coating destruction in SBF. Moreover, the osteoblast culture results suggest that the MAO/HT/PDA coating promotes cell spread and proliferation noticeably compared to both the MAO and MAO/HT coatings. This study provides compelling evidence that the Mg(OH)₂/PDA composite coating is biodegradable and offers outstanding protection for micro-arc oxidized magnesium. As a result, it holds great promise for significant applications in the field of orthopedic medicine. Full article

This work mainly explores whether the solubility product principle has a guiding role in regulating the composition of micro-arc oxidation (MAO) coatings. The MAO process was conducted on AZ31 Mg alloy in silicate electrolyte. Varying amounts of Potassium fluoride (KF) and Ammonium fluoride (NH₄F) were separately added to the basic electrolyte to regulate the OH⁻ and F⁻ contents in the electrolyte. The microstructure, phase composition and corrosion resistance of the MAO coatings prepared in different electrolytes were analyzed. Results showed that regardless of KF content, MgO was the main component for the MAO coatings obtained in electrolytes with KF. This was because the addition of KF not only elevated the F⁻ concentration in the electrolyte but also enhanced the OH⁻ concentration as a result of F⁻ hydrolysis. Based on the solubility product constants (Ksp) of MgO and MgF₂, a relatively lower concentration of Mg²⁺ was sufficient for the formation of MgO. Hence, Mg²⁺ consistently exhibited preferential reactivity with OH⁻, leading to the formation of MgO. The findings of the study demonstrated that the presence of KF electrolyte resulted in an enhancement of conductivity and an increase in the concentration of OH⁻. Conversely, the growth rate of the coating was observed to be low, and the coating-forming phases of the coating were identified as MgO and Mg₂SiO₄, and the coating had better corrosion resistance. NH₄F electrolyte with the increase in NH₄F concentration, conductivity decreases and then increases, OH⁻ concentration decreases, the growth rate of the coating is faster, the concentration of F⁻/OH⁻ is higher, the coating-forming phase is transformed into MgF₂, and the corrosion resistance of the coating is reduced. Full article

Magnesium as a biodegradable metal implant has garnered attention. Nevertheless, its rapid degradation rate and insufficient osseointegration restrict its clinical applications. In order to enhance the corrosion resistance and bioactivity of magnesium alloys, superhydrophobic hydroxyapatite (HA) layers were synthesized on micro-arc oxidized (MAO)-treated AZ31B magnesium alloy through liquid-phase deposition. This study examined the surface morphology, phase composition, bonding strength, wettability, electrochemical properties, and in vitro mineralization of the synthesized coatings. The study results demonstrated that the improved corrosion resistance of composite coatings in Hank’s solution is due to the formation of a protective HA layer. The inclusion of the MAO coating significantly enhances the bonding strength between the hydroxyapatite (HA) layer and the bare magnesium alloy. The concentration of NaH₂PO₄ affects both the microstructure and wettability. The composite coating exhibited excellent osseointegration capabilities, with new HA layers observed after immersing the samples in simulated body fluid (SBF) solution for three days. These findings suggest that the combination of MAO and solution treatment presents a promising method for enhancing biocompatibility and reducing magnesium degradation, thus making it a viable option for biodegradable implant applications. Full article

To enhance the surface protection of exposed moving parts made from magnesium alloys, this study focuses on developing high-performance micro-arc composite (MCC) coatings on AZ80 wrought magnesium alloy substrate. AZ80 alloys were fabricated through forging at different temperatures (250 °C, 350 °C, and 450 °C) to investigate the influence of thermal deformation on substrate properties. Subsequently, micro-arc oxidation (MAO) coatings and MCC coatings were applied to the forged alloys. Comprehensive analyses—including microstructural characterization, salt spray corrosion tests, and stress corrosion cracking (SCC) evaluations—were conducted under both static and stress conditions. Among the forging temperatures, 250 °C produced substrates with refined grains and a favorable distribution of β-Mg₁₇Al₁₂ precipitates, resulting in improved baseline corrosion resistance. MAO coatings offered moderate protection, primarily delaying corrosion initiation and crack propagation under stress environments. Building upon this foundation, MCC coatings—fabricated by electrostatic spraying to form an inner-embedded and outer-wrapped structure over the MAO layer—demonstrated significantly superior protective performance. Under both static and stress corrosion scenarios, the MCC coatings effectively suppressed SCC initiation and progression, highlighting their potential for robust surface protection in demanding service environments. Full article

To address the biological inertness of pure titanium implants, a composite coating with a strontium-doped hydroxyapatite (Sr-HA) phase and H₂Ti₅O₁₁·H₂O nanorods was engineered via ultrasonic-assisted micro-arc oxidation (UMAO) with hydrothermal treatment (HT). The ultrasonic field was applied to modulate the MAO discharge behavior, enhancing ion transport and coating formation. Structural characterization revealed that UMAO-HT coatings exhibited a lower anatase/rutile ratio and higher Sr-HA crystallinity, as compared to MAO-HT. In vitro simulated body immersion studies showed that UMAO-HT induced rapid apatite formation within 24 h, with a better apatite-inducing ability than the conventional MAO-HT. Density functional theory (DFT) simulations demonstrated that Sr substitution in HA lowered the (001) surface work function, enhancing Ca²⁺ adsorption energy and promoting apatite phase nucleation. This work reported the synergistic effects of ultrasonic-induced microstructure optimization and Sr-HA higher bioactivity, providing a mechanistic framework for designing next-generation bioactive coatings with enhanced osseointegration potential. Full article

In this study, a graphene oxide (GO)/zinc oxide (ZnO)/hydroxyapatite (nHAp) composite coating was constructed on a pure titanium surface by microarc oxidation (MAO) pretreatment combined with hydrothermal technology (HT), thereby making it possible to explore the performance optimization of this coating for Ti-based implants. Scanning electron microscopy (SEM), an energy dispersion spectrometer (EDS), Fourier transform infrared spectroscopy (FTIR), Ramam spectroscopy (Ramam), etc., confirmed that the GO/ZnO/nHAp composites were successfully loaded onto the pure Ti surfaces. Through nanoindentation, differential thermal analysis (DiamondTG/DTA), and dynamic polarization potential detection, the GO/ZnO/nHAp composite coating imparts excellent nanohardness (2.7 + 1.0 GPa), elastic modulus (53.5 + 1.0 GPa), thermal stability, and corrosion resistance to pure Ti implants; hemolysis rate analysis, CCK-8, alkaline phosphatase (ALP) detection, alizarin red staining, and other experiments further show that the coating improves the hemocompatibility, biocompatibility, and bone guidance of the Ti implant surface. Studies have shown that GO/ZnO/nHAp composite coatings can effectively optimize the mechanical properties, corrosion resistance, biocompatibility, and bone guidance of pure Ti implants, so that they can obtain an elastic modulus that matches human bone. Full article

A high-porosity micro-arc oxidation (MAO) functional coating was fabricated on aluminum foam substrate through micro-arc oxidation technology, developing a structurally and functionally integrated bulk catalyst support material. Orthogonal experiments were employed to determine the optimal electrical parameters for achieving maximum coating porosity, with systematic investigations into the effects of electrolyte temperature and sodium tetraborate additives on pore characteristics. The phase composition, surface morphology, and elemental distribution of the porous coating were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Mercury intrusion porosimetry was applied to quantify the total pore area and pore size distribution. By means of secondary micro-arc oxidation, the catalyst was distributed in a gradient on the coating cross-section, which greatly improved the utilization rate of the catalyst. The formation mechanism of the porous coating was discussed, and the specific surface area of the fabricated catalyst-loaded materials was as high as (1.4~6.3) × 10⁴ m²/m³, which provided a large number of attachment sites for catalyst particles. Full article

This study presents a systematic investigation into the influence of pulse frequency on the micro-arc oxidation (MAO) coating of AZ31B magnesium alloy following electron-beam remelting (EBR). The morphology, thickness, and corrosion resistance of the EBR-MAO composite coating were meticulously analyzed across various pulse frequencies (100 Hz, 200 Hz, 300 Hz, 400 Hz) employing scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical measurement techniques. The results show that as the pulse frequency escalates from 100 Hz to 400 Hz, the average thickness of the EBR-MAO composite coating diminishes from 41.1 μm to 38.5 μm, reduced by 6.7% compared to 10.4% in the MAO coating. Concurrently, the porosity exhibits a reduction from 1.93% to 1.35%, accompanied by a densification of the coating’s structure. High pulse frequencies yield coatings with enhanced smoothness and fewer defects. Notably, the corrosion resistance of the coatings demonstrates significant improvement at higher frequencies (400 Hz) compared to their lower-frequency (100 Hz) counterparts, as evidenced by a tenfold increase in corrosion current density. This research underscores the pivotal role of pulse frequency in optimizing the protective qualities of MAO coatings on magnesium alloys. Full article

This study aims to enhance the wear resistance of MAO/MoS₂ composite coatings fabricated on TC4 titanium alloy substrates through a composite process of microarc oxidation (MAO) and hydrothermal synthesis. The MAO treatment experiments were designed according to the L16 (4⁵) orthogonal array to optimize the NaAlO₂ concentration and electrical parameters (oxidation voltage, frequency, duty ratio, and treating time), with four levels for each factor. The optimized MAO process parameters were identified as a NaAlO₂ concentration of 10 g/L, an oxidation voltage of 500 V, a frequency of 200 Hz, a duty ratio of 20%, and a treating time of 30 min. The experimental results indicated a notable reduction in porosity, from 4.45% to 0.30%, in the optimized composite coating. Concurrently, there was a 43.2% increase in microhardness and a 327.9% increase in adhesive strength. Furthermore, the average coefficient of friction (CoF) of the composite coating was observed to be 0.13 at a high load of 20 N and a wear time of 20 min, representing a significant reduction of 68.5% compared to the CoF of the single MAO coating. Full article

Background/Objectives: Parkinson’s disease (PD) is a progressive neuro-degenerative disorder characterized by α-synuclein aggregation, which promotes neuronal death and accelerates neurodegeneration. Small interfering RNA (siRNA) can reduce α-synuclein levels, but its therapeutic potential is limited by poor stability and delivery challenges. Similarly, Selegiline (Sel), a monoamine oxidase-B (MAO-B) inhibitor, has low bioavailability, restricting its effectiveness. This study aims to develop an intranasal (IN) albumin-coated liposomal system (C-Lip_Sel-siSNCA2) for the co-delivery of Sel and α-synuclein-targeting siRNA (siSNCA2) to enhance brain targeting and therapeutic efficacy. Methods: Liposomes were prepared using the ethanol injection method and optimized via D-optimal design for size, charge, and encapsulation efficiency (EE%). The optimized formulation was coated with human serum albumin (HSA) and characterized for stability, cellular uptake, and gene silencing. In vivo pharmacokinetics and pharmacodynamics were assessed in a rotenone-induced PD rat model to evaluate the motor function, biochemical markers, and brain-targeting efficiency. Results: Optimized liposomes had a particle size of 113.5 ± 6.8 nm, zeta potential of 6.2 ± 0.8 mV, and high EE% (Sel: 92.35%; siRNA: 78.66%). Albumin coating increased size to 136.5 ± 10.3 nm and shifted zeta potential to −13.5 ± 1.4 mV, enhancing stability and targeting. IN administration achieved a 3-fold increase in brain area under the concentration-time curve (AUC) versus intravenous delivery. In PD rats, C-Lip_Sel-siSNCA2 improved motor and non-motor functions, restored dopamine levels, enhanced catalase activity, and reduced MAO-B levels, mitigating dopamine degradation and α-synuclein aggregation. Conclusions: This non-invasive, dual-action nanoplatform offers a targeted therapy for PD, combining siRNA gene silencing and MAO-B inhibition, with the potential for clinical translation in neurodegenerative diseases. Full article

The present study investigates the effect of different concentrations of Na₂WO₄ and graphene oxide dispersed composite additives on the structure and corrosion resistance of 6063 aluminum alloy micro-arc oxidation (MAO) coatings in a silicate electrolyte. The characterisation of the microstructure, cross-sectional morphology, elemental distribution, and phase composition of the films was conducted utilising scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The corrosion resistance of the films was tested by prolonged immersion for 24 h, 72 h, 168 h, and 240 h, with measurement of kinetic potential polarisation curves and impedance modulus in a 3.5 wt.% NaCl solution. The densification of the films was enhanced with increasing mass concentration of Na₂WO₄ and dispersed graphene oxide in the electrolyte, and the thickness initially increased and then decreased. The film containing 6 g of Na₂WO₄ and 10 mL of graphene oxide dispersion (G10-6) exhibited optimal densification and thickness, with an I_corr value of 3.01 × 10⁻⁶ A·cm⁻² and a low-frequency impedance film value of 10⁸ Ω·cm², thereby demonstrating the most advanced corrosion resistance among the films. The densification and corrosion resistance of the films were enhanced by the incorporation of Na₂WO₄ and graphene oxide dispersion into the alkaline electrolyte. Full article

As one of the lightest metallic structural materials, magnesium (Mg) alloys possess numerous distinctive properties and are utilized across a broad spectrum of applications. However, the poor corrosion resistance of Mg alloys limits their application. Micro-arc oxidation (MAO) is an effective surface treatment method that enhances the corrosion resistance of Mg alloys. Nevertheless, the intrinsic porous structure of MAO coatings hinders significant improvement in corrosion resistance. Research indicates that the pre- and post-treatment processes associated with MAO markedly enhance the densification of the oxide coatings, thereby improving their overall performance. This paper aims to provide a comprehensive review and analysis of the effects of various pre- and post-treatment processes, highlighting key advancements and research gaps in improving MAO coatings on Mg alloys. An in-depth analysis of the crucial role of pre-treatment in optimizing interfacial bonding and post-treatment in enhancing coating density is conducted using electrochemical testing and scanning electron microscopy (SEM). Finally, the future development of pre- and post-treatment processes are discussed. Full article